dark and light areas on car panels
A simple subdivision surface fixes this:


This is caused due to some faces being bigger than others, and as such Blender reflects the light differently. This happens when smooth shading is enabled, and the angle/size of two or more faces right next to each other differ greatly.

If using a subdivision surface modifier is not suitable to you (This should work with Blender Game engine as well), modifying the faces may be your best bet.

Hope this helps.